The present invention relates to a device for transferring the thrust of an actuator, an injection valve with such a device, and a method for manufacturing a tappet, such as may be used in such a device.
U.S. Pat. No. 4,101,076 to Bart discloses a conventional fuel injection valve which directly operates a fuel injector needle through a mechanical tappet. The tappet has two lever arms of different length, which are arranged at right angles to one another and are joined together at a bearing area. The shorter lever arm is associated with the piezoelectric actuator and the longer lever arm with the injector needle. The tappet is fulcrumed in the bearing area on the housing of the fuel injection valve. The thrust of the piezoelectric actuator is converted by the different lengths of the two lever arms to a greater thrust of the injection needle.
These conventional valves suffer from a number of disadvantages, including the fact that their tappets are insufficiently stiff, which leads to inaccuracy in the transfer of the thrust, especially in the case of highly dynamic operations.
The present invention provides a device for transferring the thrust of an actuator, which is simple in design and can be manufactured at low cost. An important advantage of the present invention lies in the shape of the tappet, which assures great rigidity, thereby ensuring that thrust is directly transferred, even in highly dynamic processes. Another advantage of the present invention is that the tappets can be manufactured with great accuracy and precision.
The present invention is achieved by providing a device for transferring thrust between an actuator and a plunger. The actuator moves a first displacement relative to a body, and the plunger moves a second displacement relative to the body. The device comprises a tappet having a first end face, a second end face spaced along an axis from the first end face, and a cylindrical surface surrounding the axis and extending between the first and second end faces, the cylindrical surface having a first contact portion adapted for contiguously engaging the body, a second contact portion adapted for contiguously engaging the actuator, and a third contact portion adapted for contiguously engaging the plunger; and a guide having first and second surfaces, the first surface confronting the first end face and the second surface confronting the second end face such that movement of the tappet along the axis is substantially prevented.
The present invention is also achieved by providing an injector for supplying fuel to a combustion chamber. The injector comprises a body; an actuator generating a thrust with respect to the body; a plunger displaceable with respect to the body by the thrust; a tappet transferring the thrust from the actuator to the plunger; and a guide. The tappet has a first end face, a second end face spaced along an axis from the first end face, and a cylindrical surface surrounding the axis and extending between the first and second end faces. The cylindrical surface has a first contact portion contiguously engaging the body, a second contact portion contiguously engaging the actuator, and a third contact portion contiguously engaging the plunger. The guide has a first surface confronting the first end face and a second surface confronting the second end face, such that movement of the tappet along the axis is substantially prevented.
The present invention is further achieved by providing a method of producing a tappet. The tappet has a first end face, a second end face spaced along an axis from the first end face, and a cylindrical surface surrounding the axis and extending between the first and second end faces. The cylindrical surface has a first contact portion contiguously engaging a body, a second contact portion contiguously engaging an actuator, and a third contact portion contiguously engaging a plunger. The method comprises providing an elongated, right-circular cylindrical rod; machining the rod lengthwise such that a transverse cross-sectional shape of the rod corresponds to a desired shape of the end faces; and cutting the rod transversely so as to provide a plurality of the tappets.